Critics say it's a chemical that could cause infertility or cancer, while others see it speeding the growth of super weeds and causing worrying changes to plants and soil. Backers say it is safe and has made a big contribution to food production.

It's glyphosate, the key - but controversial - ingredient in Roundup herbicide and the top selling weed killer used worldwide. For more than 30 years, glyphosate has been embraced for its ability to make farming easier by wiping out weeds in corn, soybean and cotton fields, and for keeping gardens and golf courses pristine.

But the chemical touted as a safe, affordable and critical part of global food production, is now at a crossroads.

Amid rising voices of alarm, regulators in the United States and Canada are conducting a formal review of glyphosate's safety, lawsuits are pending and some groups are calling for a global ban.

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"Glyphosate's days are numbered," said Paul Achitoff, a lawyer for Earthjustice, an environmental law firm that last month sued the U.S. Department of Agriculture in part over concerns about heavy glyphosate use.

Agricultural seeds and chemicals giant Monsanto Co introduced the chemical to the world in 1974 and has made billions of dollars over the years from Roundup as well as from the "Roundup Ready" corn, soybeans and cotton the company has genetically engineered to survive dousings of glyphosate.

Last year alone, Monsanto made more than $2 billion in sales of Roundup and other glyphosate-based herbicides, though revenues have been in decline amid competition from generic makers since the company's glyphosate patent expired in 2000.